Pulse-actuated strip line ferrite circulator switch utilizing residual magnetization to eliminate holding current



L. FREIBERG PULSE-ACTUATED STRIP LINE FERRITE CIRCULATOR SWITCH UTILIZING RESIDUAL MAGNETIZATION To ELIMINATE HOLDING CURRENT Filed April 50. 1962 3 Sheets-Sheet l 'I Af/ 3'1/5/25 www@ /9 37 Z7 35 4Z Z5 :51E- P CURREA/f Pif/LSE DE VICE 24 EI IE!" 2n 0 Peg/afge INVENTOR.

May 25, 1965 I FRI-:BERG 3,185,941

PULSE-ACTUATED STRIP LINE FERRITE CIRCULATOR SWITCH UTILIZING RESIDUAL MAGNETIZATION TO ELIMINATE HOLDING CURRENT Filed April 30, 1962 5 Sheets-Sheet 2 RHEMFRGY E av Es L50 fk5/55H6 IN V EN TOR.

May 25, 1965 FRL-335m; 3,185,941

PULSE-ACTUATED STRIP LINE FERRITE CIRCULA'IOR SWITCH UTILIZING RESIDUAL MAGNETIZATION TO ELIMINATE HOLDING CURRENT Filed April 30, 1962 5 Sheets-Sheet 3 DB--r INSERTION Sla. -P 3l LOSS 3/c SIb xxx 3/b *P3/a. 00o

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zooo 2oso` 2460 FPEQ-MC-P- f1 E. E E0 FEE/BEE@ INVENTOR.

United States Patent O 3,185,941 PULSE-ACTUATED STRlP LiNE FERRITE CRCU- LATOR SWITCH UTlLIZING RESIDUAL MAG- llPTqIrlrZATION T ELMENATE HOLDING CUR- Leo Freiberg, San Jose, Calif., assigner to Lockheed Aircraft Corporation, Burbank, Calif. Filed Aprrt), 1962, Ser. No. 191,358 2 Claims. (Cl. S33-1.1)

The present invention relates to a circulator switch and more particularly to a pulse-actuated circulator switch which eliminates the necessity of holding current and pro- 'vides minimum magnetic reluctance.

One of the major disadvantages of employing a circulator as a microwave switch has been the requirement of holding current to maintain the circulator in the switched position.V That is, prior circulators have required the use of continuous current through an electromagnet to maintain switching in a predetermined mode. To reverse the switching mode or the direction of circulation, the current is reversed through the electromagnet. Again, however, it is necessary to maintain continuous current in this reversed direction to maintain this reversed switching mode. The primary disadvantage of this technique is the large amount of power consumed due to the continuous current requirement. This becomes especially critical in space applications where operation may be required over several months or years and only a small amount of power is available.

The present invention obviates this disadvantage by employing a switchable magnetic material which magnetizes upon the application of a current pulse in one direction and retains this direction of magnetization after the pulse has been removed. Opposite polarity or switching mode is obtained by applying a current pulse of opposite polarity. In this manner the only power required is during the switching interval when the pulse is being applied thereby obviating the large power consumption of holding current.

After this switching pulse has been removed, the switch will theoretically remain indetinitely in the selected mode and in actual practice it has never been found necessary to reapply a pulse to maintain the switch in the selected mode.

This has been accomplished by the unique utilization of a material having a coercive force such that the magnetization may be reversed with a current pulse of reasonable magnitude and still have the proper amount of retentitivity at the termination of the current pulse. In addition, the present invention provides a closed loop magneticpath that provides minimum magnetic reluctance thereby resulting in minimum current or power requirement as well as making it possible to operate at a higher frequency for a given current pulse.

Accordingly, an object of the present invention is to provide a low power consuming circulator switch.

Another object of the present invention is to provide a pulse-actuated circulator switch which eliminates the necessity of holding current.

A further object of the present invention is to provide a circulator switch which will indenitely remain in a selected switched position without re-pulsing or using a holding current.

A still further object oi the present invention is to provide a pulse actuated circulator switch employing a material having a coercive force such that the magnetization may be reversed with a current pulse of reasonable magnitude and still have the proper amount of retentivity at the termination of the current pulse.

A still further object of the present invention is to proldl Patented May 25, 1965 'ice vide a pulse actuated ferrite switch having a closed loop magnetic path that provides minimum magnetic reluctance thereby resulting in minimum current or power requirement as well as making it possible to operate at a higher frequency for a given current pulse.

The specific nature of the invention, as well as other objects, uses and advantages therof, will clearly appear from the following description and from the accompanying drawing in which:

FIGURE 1 is a'top elevation, partly in section, of the pulse actuated circulator` switch of the present invention.

FlGURE 2 is a side elevation of the circulator switch shown in yFGURE 1. i

AFIGURE 3 is a sectional View of the circulator switch shown in FlGURE l.

FIGURES 4A and 4B are illustrations of the strip-line ymember of the circulator switch shown in FIGURES 1 through 3 and depicts the switching action during the two modes of operation.

FIGURE 5 is a diagram illustrating the B-H characteristie of the electromagnetic core material during diiierent conditions of operation.

FIGURE 6 is a diagram illustrating theinterrelation of the applied input pulses and the microwave switching in the to output legs of the circulator switch.

FXGURE 7 is a family of curves illustrating isolation or power leakage into the non-switched arm.

FIGURE 8 is a family of curves illustrating insertion loss or the sum of the reflected and internally consumed power.

FIGURE 9 is a family of curves illustrating the VSWR (voltage standing wave ratio) or the energy reected back into the input leg.

Like numerals designate like elements throughout the tigures of the drawing.

ln FIGURES 1 and 2 are illustrated the pulse actuated circulator switch 11 of the present invention. `Switch 11 includes top plate 13 and bottom plate 15 both of which have concentric openings formed therein for receipt of cores 17 and 19, respectively. Preferably the diameters of the openings in plates 13 and 15 and the diameters of cores 17 and 19 are selected for press fitting thereby eliminating the necessity of mechanical or adhesive interconnections. Plates i3 and 1S are connected to annular side member 21 by means of screws 23 or the like resulting in the formation of cylindrical cavity 24 formed between the interior surfaces thereof.

yCores 17 and 19 are wound by wire 25 and in the same direction such that opposite polarity of the adjacent faces results upon the application of a current pulse havinga predetermined polarity as generally depicted in kFIGURE 3. The outer faces of cores 17 and 19 are series connected rby means of U-shaped bracket 27 to provide a closed magnetic loop the lfunction of which will hereinafter become apparent. Bracket 27 is preferably made of material having a low reluctance, such asv Soft iron.

Disposed within cylindrical cavity 24 is strip-line member 29 having conductor legs 31a, 31h and 31e and junction 33 of the shape substantially as shown. The ends of these conductor legs are connected to terminal pins 35 of connector plugs 37 as by means of solder or the like. It will be particularly noted that strip line member 29 is made of soft iron which is then thinly coated with a material having high conductivity such as silver. The thickness of the coating is of the order of about .0005 inch. As will hereinafter become apparent, it iS critical that the base material be made of soft iron or the like since it provides a low reluctance and it is critical that the soft iron, which has poor microwave transmitting characteristics, be coated with silver or the like since silver has high microwave transmitting characteristics which is essential for strip-line transmission in the frenecessary magnetic characteristics.

, surface of strip line member 29. Although the reluctanceV Y of the magnetic path issomewhat increased, the end surfaces of members 41 and 42 are connected to the opposite surfaces of stripline member 29 byzan extremely thin Y adhesive suchas epoxy resin having mixed therewith a mlaterial having-'a low reluctance.` An adhesive is generally not necessary'to connect the inner surfaces of Ycore 17 :and 19 to members 41 and 42 since, upon assembly, intimate surface contact may be realized by simultaneous force fitting cores 17 and 19.

The magnetic characteristics of cores 17 and 19 are criticalfeatures of the present invention. It has been found that it is possible to obtain continuous switching by the application of a short time duration pulse to lead wires 25 by'means of current pulse device 45 provided the material'from which cores 17 and 19 are made have the It has been found that SAE 4130 steel has the necessary retentivity as well as coercive force characteristics. The coercive force of the magnetic material must be such that the retentivity, or remanent magnetization, may be reversed with a current lpulse of .reasonable magnitude and still have the proper amount of retentivity at ythe termination of the current pulse. The required switching current pulse depends upon the closed loop circuit reluctance which is highly dependent upon the materials forming the closed loop circuit.

Itis necessary to form members 41 and 42 from ferrite material in order to obtain circulator or switching action. The symmetrical junction, in theabsence of the biased ferrite material, normally divides incoming high frequency energy equally between-the remaining two arms. However, when magnetically biased ferrite material is added to lthe junction, high frequency energy entering any terminal is all directed to rthe adjacent terminal, the selected terminal being determined by the direction of the magnetic biasing lield. During switching, the ferrite material has a low reluctance and after it has become switched or saturated, the reluctance becomes relatively large. However, since the reluctance is low during switching, the power or current required for switching is not excessive.

Operation v 19 will possess' a predetermined 'amount of retentivity as will hereinafter be explained with relation to FIGURE 5. j Upon the application of a negative current pulse, the`configuration-of thelines of force will remain the same; however, the directionV will be reversed.

It will be noted that the diameter of members 17 and -19 is large compared lto the elfective diameter of junction of a negative pulse wherein the vcrosses indicate the eld is entering the plane of the paper.

In order to more fully appreciate the unique features of the present invention, it is believed the following analysis is pertinent: It should be initially pointed Vout that the operating frequency of thefiabove-described circulator switch is a function of several parameters which'include (l) diameter of the ferrite, (2) type of ferrite material, (3) thickness of the ferrite, (4) Vwidth of strip line member, (5) configuration of junction 33 and (6) retentivity or biasing gauss. The latter parameter (6) is perhaps the most critical inasmuch as the realization Vof suiciently high frequency of operation is: highly dependent upon adequate biasing gauss. t

The retentivity may bejdetermined from the relationship: Y Y l MMF I" R where p is the total flux passing through core material 17 or 19, MMF is the magnetomotive force in oersteds H (where H :KNI where K is a constant and NI is the'ampere turns -of windings 25) and R Vis the reluctance. Knowing the total liux, the retentivi-ty biasing gaussB may be readilydetermined from the relation l B A where A is the area of the core material. p

FIGURE 5 includes a family of curves denoted as I and II illustrating the B'-H characteristics of core 17 and 19 during different conditions of operations. As previously explained, for minimum power and maximum frequency, it is desirable to have maximum retentivity. With a given pulse current, curve I will be the characteristic curveV when the closed loop magnetic reluctance is apredetermined amount and curve II will result when the closed loop magnetic reluctance is larger than this predetermined amount. It can therefore be seen that maximum retentivity is obtained with minimum reluctance and this is realized by the present invention as previously explained. It will be noted that upon removal of the current pulse, the operating point on the B-H loop will beat some position between points a and 1a. If the reluctance is low, the operating point may be at point c, whereas, if the reluctance is high, the operating point may be at point It can therefore be seen that it is desirable to have minimum reluctance.

33. This yrelationship is highly desirable since the lines of l force would otherwise enter strip line member 29 at an n angle other than 90 resulting in an undesirable non-uniformfield at junction 33.

. FIGURE 4A depicts the switching direction of the microwave energy .upon the application of a positive pulse wherein the small circles indicate ythe field is leaving the plane of the paper. FIGURE 4B depicts the switching "direction of the-microwave energy upon the application point To reverse the iield direction, a Apulse of opposite polarity is applied which changes the operating point to and upon termination of the pulse the operating point will reside at somerposition, Vdepending upon the reluctance, between points fg and h.

In FIGURE 6 is illustrated anv actual reproduction of an oscilloscope Vtrace showing the pulse actuated switching actionfof the present invention. FIGURE 6A depicts sequential positive and negative current pulses applied to windings 25 from current pulsedevice 45.A The microwave output from legs 31b and 31C is shown in FIGURE 6B and FIGURE`6C, respectively. These traces werel obtained by the use of iive ampere current pulses which are suliieient to reverse the magnetization and obtain a magnetic field retentivity of 200` gauss. vPulse widths of 140 milliseconds were used; however, since the switching time of the' core material is about five milliseconds, pulse widths of ten milliseconds are suflicient. Faster switching times may be obtained by reducing the number of turns about cores 17 and 19.V Y

FIGURES 7, 8 and9 illustrate the characteristics ,of the circulator switch biased only by the remanent magnetization of cores 17 and 19. FIGURE 7 is a family of curves illustrating isolation or power leakage into the nonswitched arm,` FIGURE 8 is a family of curves illustrating insertion loss or the sum of the reflected and internally consumed power and FIGURE 9 is a family of curves illustrating the VSWR (voltage standing wave ratio) or the energy reected back into the input leg. The operating condition of each of the curves of FIG- URES 7 through 9 is self explanatory from the symbols and corresponding legends affixed thereto.

lt is to be understood in connection with this invention that the embodiment shown is only exemplary, and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims. For example, this circular switch may be employed over the entire microwave spectrum ,and various dimensions and coniigurations of elements will be employed depending upon the selected frequency of operation. Similarly, the dimensions and congurations of elements may be changed at a predetermined frequency and still remain within the scope of the present invention. In addition, it will be obvious to one skilled in the art that the above described biasing technique may be used in conjunction with a Faraday rotation circulator or a differential phase shift circulator to provide a circulator switch.

What is claimed is:

1. A microwave switch comprising means forming a cavity, an input communicating with said cavity, first and second outputs communicating with said cavity, a member disposed in said cavity and having first, second and third legs connected to a common junction, the other ends of said rst, second and third legs respectively connected to said input and first and second outputs, first and second members operatively connected to said means and located on opposite sides of said common junction, ferrite material in facial contact with said first member and one side of said junction, ferrite material in facial contact with said second member and the other side of said junction, said first and second members consisting of switchable magnetic SAE 4130 steel which retains residual magnetization upon being switched, windings disposed about said first and second members, means operatively connected to said windings for applying positive and negative current pulses, whereby after the application of a positive current pulse said first and second members retain residual magnetization and provide a eld in a rst direction through said junction resulting in the transmission of a microwave signal from said input to said first output and after the application of a negative current pulse said first and second members retain residual magnetization and provide a field in a direction opposite to said first direction through said junction resulting in the transmission of a microwave signal from said input to said second output.

2, A microwave switch comprising means forming a cavity, an input communicating with said cavity, first and second outputs communicating with said cavity, a member disposed in said cavity and having first, second and third legs connected to a common junction, said member being formed of a material having a low reluctance and coated with a material having high conductivity, the other ends of said first, second and third legs respectively connected to said input and first and second outputs, vfirst and second members operatively connected to said means and located on opposite sides of said common junction, ferrite material in facial contact with said irst member and one side of said junction, ferrite material in facial contact with said second member and the other side of said junction, said first and second members consisting of switchable magnetic SAE 4130 steel which retains residual magnetization upon being switched, windings disposed about said rst and second members, means operatively connected to said windings for applying positive and negative current pulses, means interconnecting said first and second members made of a material having a low reluctance, whereby after the application of a positive current pulse said first and second members retain residual magnetization and provide a field in a irst direction through said junction resulting in the transmission of a microwave signal from said input to said first output and after the application of a negative current pulse said first and second members retain residual magnetization and provide a field in a direction opposite to said first direction through said junction resulting in the transmission of a microwave signal from said input to said second r output.

References Cited by the Examiner UNITED STATES PATENTS 3,015,787 1/62 Allin et al. 333--1 3,063,024 1l/62 Davis 333-1 3,079,570 2/ 63 Hickly 333-1 3,085,212 4/63 Clark et al 333-1 HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner. 

1. A MICROWAVE SWITCH COMPRISING MEANS FORMING A CAVITY, AN INPUT COMMUNICATING WITH SAID CAVITY, FIRST AND SECOND OUTPUTS COMMUNICATING WITH SAID CAVITY, A MEMBER DISPOSED IN SAID CAVITY AND HAVING FIRST, SECOND AND THIRD LEGS CONNECTED TO A COMMON JUNCTION, THE OTHER ENDS OF SAID FIRST, SECOND AND THIRD LEGS RESPECTIVELY CONNECTED TO SAID INPUT AND FIRST AND SECOND OUTPUTS, FIRST AND SECOND MEMBERS OPERATIVELY CONNECTED TO SAID MEANS AND LOCATED ON OPPOSITE SIDES OF SAID COMMON JUNCTION, FERRITE MATERIAL IN FACIAL CONTACT WITH SAID FIRST MEMBER AND ONE SIDE OF SAID JUNCTION, FERRITE MATERIAL IN FACIAL CONTACT WITH SAID SECOND MEMBER AND THE OTHER SIDE OF SAID JUNCTION, SAID FIRST AND SECOND MEMBERS CONSISTING OF SWITCHABLE MAGNETIC SAE 4130 STEEL WHICH RETAINS RESIDUAL MAGNETIZATION UPON BEING SWITCHED, WINDINGS DISPOSED ABOUT SAID FIRST 